1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head for use in thermally-assisted magnetic recording where a recording medium is irradiated with near-field light to lower the coercivity of the recording medium for data writing.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head section including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head section including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider that flies slightly above the surface of a recording medium. The slider has a medium facing surface that faces the recording medium.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To solve the foregoing problems, there has been proposed a technology so-called thermally-assisted magnetic recording. The technology uses a recording medium having high coercivity. When writing data, a write magnetic field and heat are simultaneously applied to the area of the recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with laser light. The plasmon generator has a near-field light generating part located in the medium facing surface. The laser light to be used for generating near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near the medium facing surface of the slider.
JP-A-2011-86361 discloses a thermally-assisted magnetic recording head configured to excite plasmons on a plasmon generator (a light emitting part) by directly irradiating the plasmon generator with laser light.
U.S. Patent Application Publication No. 2010/0172220 A1 discloses a thermally-assisted magnetic recording head in which a plasmon generator (a surface plasmon antenna) is arranged to face the outer surface of a waveguide (a core) with a predetermined spacing therebetween, so that light propagating through the waveguide is totally reflected at the outer surface of the waveguide to thereby generate evanescent light that is used to excite surface plasmons on the plasmon generator.
Thermally-assisted magnetic recording typically uses a main pole, a return path section, and a coil as means for producing a write magnetic field. The main pole and the return path section each have an end face located in the medium facing surface. The main pole produces a write magnetic field from its end face. The return path section is connected to the main pole so that a space through which part of the coil passes is defined by the main pole and the return path section. The coil produces a magnetic field corresponding to data to be written on a recording medium. The main pole and the return path section form a magnetic path for passing a magnetic flux corresponding to the magnetic field produced by the coil.
Now, consider a thermally-assisted magnetic recording head configured so that the near-field light generating part of the plasmon generator is interposed between the end face of the main pole and the end face of the return path section, and the core of the waveguide and the return path section intersect each other without contacting each other. JP-A-2011-86361 describes two methods for precluding the contact between the core and the return path section. The first method is to branch a portion of the core intersecting the return path section into two portions so as to detour around the return path section and then merge the two portions into one. The second method is to provide a portion of the return path section intersecting the core with a penetrating hole for passing the core therethrough. In other words, the second method is to branch the portion of the return path section intersecting the core into two portions so as to detour around the core and then merge the two portions into one.
To preclude the contact between the core and the return path section, the second method described above is typically used. In this case, the return path section includes a coupling portion for coupling the two branched portions. The coil is wound around the coupling portion.
In the above-described configuration, the width of the coupling portion in the track width direction is equal to or greater than the distance between the respective outer ends of the two branched portions in the track width direction, and is thus comparatively great. Since the coil is wound around the coupling portion, the entire length of the coil is long. As a result, the coil has a high resistance and thus has a high heating value. This causes components around the coil to expand, thus causing part of the medium facing surface to protrude toward a recording medium and become more likely to collide with the recording medium. In order to prevent this, the distance between the medium facing surface and the recording medium could be increased. However, this would lead to deterioration in write characteristics such as the overwrite property or to an increase in error rate.
On the other hand, in order to improve the write characteristics in a high frequency band, it is desirable to reduce the length of the magnetic path formed by the main pole and the return path section. To that end, it is effective to bring the portion of the return path section intersecting the core closer to the medium facing surface. Here, consider a case where the coil is wound around the coupling portion of the return path section. In this case, since the width of the coupling portion in the track width direction is comparatively great as mentioned above, the coil has at least one conductor portion that is located between the coupling portion and the medium facing surface and extends linearly in parallel to the medium facing surface (such a conductor portion will hereinafter be referred to as a linear conductor portion). If the portion of the return path section intersecting the core is brought closer to the medium facing surface, the linear conductor portion becomes narrow and long. This makes the coil higher in resistance, thus causing the above-described various problems to occur noticeably.